Yamaha TRX850 Enthusiasts Forum

Hi guys, just would like to get some ideas on where to start my search for a problem I just had yesterday at the track.
Here's a run down on what happened in the day, It stared out very wet on track, bike was running fine, midday came and it dried out quick, then i went to slicks. From here on the bike started to play up, first it sounded like the engine got louder, and also made a slight knocking sound, and didn't want to rev as hard at the top peak rev. Coming down the straight in that session it just died for two seconds then came back to life. Before I come back in to the pits I thought I damaged something in the motor from the knocking sound, but in the pits it sounded alright. At a stand still revving it sound ok, just a delayed reaction to throttling of idle.
I went out for the last race and it was making the same noises but was still able to complete the race reasonably. Coming back into the pits for the last time, was the worst of it, it was cutting in and out badly. I let it sit for a few moments started her again and almost sounded normal, just delayed reaction as before.
My first guess is it has to be something electrical, witch could have caused the knocking, by affecting the firing. And a reason for the cutting in and out. But where do I start. Am I wrong, possibility of fuel? Just a coincidence of the rain is all.
Could the water have sat somewhere to cause this?
Any advise on where to start for the process of elimination would be greatly appreciated. Cheers

I had a similar issue when I rebuilt the bike and I shifted the spark plug leads as 1 was sitting right next to the thermo fan.
As soon as I centralised it away from anything for it to earth out against. Wet weather riding was no longer an issue.
When I put the motor back in the frame the other month the same problem re occurred and found the lead up against the thermos fan body once again.

Get some dielectric grease and seal all connectors to keep moisture out too as an added extra form of protection.
http://www.w8ji.com/dielectric_grease_v ... grease.htm

Was it wide open throttle you found the issues????
Are you running a foam sox over the bellmouths???
If saturated with moisture it may have restricted air flow causing hesitation.
While at it just check the main air jets too by the air intake side.

Try and keep the bottom of the ramair sox as high up as possible close to the bell so there is plenty of free air between the top of the sox and the top of the bell mouth.
You can draw air from the sides as well as the top of the sox this way.
If the sox is pushed down against the carby body/intake , it's restricting air flow by drawing air through the top of the sox only.

Check the calibration on your TPS too Adrian.
Take 10 minutes to Dump the oil from the bottom sump/engine case and just check for any contamination or water and check your rad fluid levels and expansion tank as a safe guard too. If all good place the 500ml oil back in the motor.
Did the mechanic re tension the head after start up/first run to operating temp/ cool down??? (composite gaskets)
Loosen 1 head bolt 1/4 turn then re tension and move on to the next bolt...